"Left channel is out" is kind of a broad statement. I assume you have no sound from the left channel, regardless of whether you're using the "A" of "B" speaker terminals? I also assume you have no sound from the left channel, regardless of whether you have AM, FM, Aux or Phono selected? The first thing is usually to flip all the switches - tape 1, tape 2, loudness, stereo/mono, etc and rotate the pots/selector switches - bass, treble,input selector and speaker selector several times to see if there's sound coming from the left channel - even briefly. If you hear anything from the left channel, you at least know the amp section is working and you have some dirty pots/switches. If you don't hear anything, you really haven't learned anything, yet but, in either case, the next step would be to clean all the pots and switches with some deoxidation spray like DeOxit.